Those exposed forget 1 out of every 5 things their unexposed peers would recall

Northumbria University, located near Newcastle in the Northeastern coast of England, has produced a cautionary study warning that second-hand smoke may lead to memory loss.

Published [abstract] in the peer-reviewed journal Addiction, the work by Psychologists Drs. Tom Heffernan and Terence O'Neil compared 27 second-hand smokers (SHS), 27 current-smokers (CS), and 29 non-second-hand smokers (non-SHS). Participants were subjected to the Cambridge Prospective Memory Test (CAMPROMPT), a common memory test. The researchers took into consideration age, other drug use, mood, and IQ, in an effort to narrow the correlation down to smoke inhalation or lack thereof.

Current smokers fared the worst on the test, recalling approximately 25-30 percent less than their non-exposed peers in time- and event-based tasks. But somewhat more surprising, the researchers also observed a time-based memory gap in those exposed to second-hand smoke. They recalled over 15 percent less than their non-exposed peers. Interestingly, memory was not affected in event-based tasks.

The authors conclude:

In a sample of never-smoked adults, exposure to SHS is associated with increased time- based, but not event-based objective PM impairments when compared with a Non-SHS group, but not to the same level of impairments as observed in current smokers. Given the concerns raised by the World Health Organisation in relation to the global impact of current smoking and exposure to SHS upon a range of health measures and other indices this is a topic that is of major public interest. Despite this, there is little in the way of systematic study on what impact exposure SHS has on everyday remembering, with the findings presented here representing the first in this line of research.

At an applied level, the findings from the present study could be incorporated into campaigns that alert people to the dangers of exposure to SHS beyond health indices and highlighting the everyday cognitive consequences of such exposure. Clearly the findings from this exploratory study could be integrated into such initiatives.

The second-hand smokers in the study were exposed to, on average, 25 hours a week (3.6 hr. per day) for 4 and 1/2 years.

As with other studies on drug abuse, it's important to note that the observed phenomena was merely a correlation -- how exactly smoke affects the brain is very poorly understood, beyond basic reward circuitry.

There are many compelling questions raised by the study. The biggest is how exactly the memory impairment works on a neurological level. Another major question is whether so-called "third-hand" smoke -- smoke absorbed by a building occupied by a heavy smoker -- could have a similar, but smaller affect. Some studies have suggested that this may be the case with other smoking-related health issues.

Alcohol has been linked to similar memory impairment (though recent studies rebuke the hypothesis of brain cell death). However, there is no second-hand analogy with alcohol. On the other hand marijuana has been linked to short-term memory loss. Given the poor understanding of second-hand (tobacco) smoke and memory loss with tobacco (the NU paper claims to be the first study on the topic), the impact of second-hand marijuana smoke is likely poorly misunderstood.

It's clear that you should be careful what you inhale -- there is compelling evidence that it could damage your memory or cause other adverse affects, though researchers in some cases aren't sure quite how that process occurs.